Computer science notes: OSI 7 layers, VLAN, DHCP, NAT

OSI7 Layer

Application (Layer 7) - Application layer

• Related to internet application services such as HTTP and SMTP

• The layer closest to the user, acting as the interface

• Handles information exchange between application processes

Presentation (Layer 6) - Presentation layer

• The layer that decides how data is represented

• Data encryption and decryption

Session (Layer 5) - Session layer

• Provides interaction and synchronization between communicating devices

• Manages data exchange in a connection session and recovery when errors occur

Transport (Layer 4) - Transport layer

• Handles reliable and accurate end-to-end data transfer

• Performs error detection and recovery, flow control, duplicate checks, and so on, to transfer data reliably and efficiently between sender and receiver

• Uses port numbers to transfer data (TCP and UDP are the main protocols)

• The data unit at the transport layer is the segment

Network (Layer 3) - Network layer

• IP communication, routing

• Manages sending data to other networks and communicates using IP addresses

• Handles routing along the way when communicating from the source IP to the destination IP

• When data is large, splits it, sends it, and reassembles it into the message

Data Link (Layer 2) - Data link layer

• Related to Ethernet, MAC communication, error detection, and retransmission

• The second layer of the OSI 7 layers, providing the functions and procedures for sending data between adjacent nodes

• Detects and corrects errors that occur in the physical layer

• Ethernet is the main protocol, and the equipment used is the switch

Physical (Layer 1) - Physical layer

• The first layer of the OSI 7 layers, expressed as hardware

• Defines the electrical and mechanical properties and the transmission media of network devices

• Made up of communication devices, connectors, circuits that send and receive, and so on

• The cable types mostly used are Coaxial, TP, and Fiber

• Data is mostly measured in bit, KB, MB, GB, and TB

• The capacity of physical layer equipment is usually described by Bandwidth, Throughput, and Backplane

VLAN

• A technology that builds a logical, virtual LAN instead of a physical setup

• Managed separately per broadcast domain to block unnecessary data

• The LAN group can't change along with a host's physical move

• No need to buy a physical switch when adding a new LAN

DHCP

• DHCP is a protocol that dynamically assigns IP addresses to clients

• Hosts whose IP changes often are easy to manage with DHCP

• Can prevent failures caused by wrong IP settings

• Can maximize efficiency by assigning an IP address only when there is a request

NAT

• A technology that connects a private IP network and translates it into a routable public IP

• The internal network setup can change without affecting the public IP range

• Maintenance costs go down because public IPs no longer need to be assigned